Resistance random access memory (RRAM) has a very low voltage switching resistance and may be used as a non-volatile memory resistor in large scale memory arrays. Unfortunately, a single RRAM memory cell is not suitable for use in a cross-point memory array.
U.S. Pat. No. 6,753,561 B1, to Rinerson et al., granted Jun. 22, 2004, for Cross point memory array using multiple thin films, describes a memory array which includes a first group of substantially parallel conductive array lines, a second group of substantially parallel conductive array lines and a plurality of memory plugs. The second group of substantially parallel conductive array lines are oriented to be substantially perpendicular to the first group of parallel conductive lines and the plurality of memory plugs are located at the intersections of the first group of parallel conductive array lines and the second group of parallel conductive array lines. Each memory plug includes multiple layers of thin films, including a thin film layer of a memory element and at least one thin film layer constituting a non-ohmic device, comprising a metal-insulator-metal (MIM) device. Insertion of a current limiter in each of the memory resistor has been proposed by Rinerson et al., supra, to resolve this problem. However, the current limiter increases the process complicity and the circuit reliability.
An equivalent circuit of a prior art cross-point memory array is shown in FIG. 1, generally at 10, wherein an array having bit lines, B1, B2, B3 and B4, cross talk paths is shown. When a voltage, VR, is applied to a word line, a resistor, e.g., R34, on bit line B4 is programmed, however, cross-talk is generated between B4 and adjacent bit lines. Bit line cross talk is a very serious problem, because cross talk may completely distort memory signal output.
A Sharp Laboratories of America internal document of S. T. Hsu et al., for and T. K. Li, for Very High Density Cross-Point Resistor Memory Array with MSM/PCMO memory cell, submitted on May 5, 2005, discloses a metal-semiconductor-metal (MSM) current limiter which is inserted to each memory cell. The MSM described in that document has back-to-back Schottky diodes and is able to handle larger current than the MIM diodes of Rinerson et al., supra.